Resonator for medical device

ABSTRACT

A resonator device including an induction coil, a conductive member positioned adjacent the induction coil, and a dielectric layer between at least a portion of the induction coil and the conductive member to form a capacitor structure. In one embodiment, the conductive member can be a stent. In an alternative embodiment, the conductive member can be a conductive film. In an additional embodiment, the dielectric layer can have a dielectric constant that changes in a predetermined fashion between at least a portion of the induction coil and the conductive member to allow for a uniform current distribution in the resonator device. The dielectric layer can also include a flexible elongate body.

This application is a Continuation of U.S. application Ser. No.11/189,526 entitled “Resonator for Medical Device” filed on Jul. 26,2005, and which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to medical device apparatus,systems, and methods; and more particularly to medical device apparatus,systems, and methods for use during magnetic resonance imaging.

BACKGROUND

Stents and other metallic implants can cause artifacts in magneticresonance (MR) images due in part to distortions in the magnetic field.Distortions in the magnetic field are often caused by the shape of thestent that acts to partially shield a radio frequency (RF) fieldgenerated during the MR procedure. This shielding of the RF field isknown as the Faraday Effect and is caused by structures, such as stents,that have a “Faraday Cage” configuration.

Generally, a Faraday Cage configuration prevents an RF field frompenetrating to the interior of such a structure. Because stents are notideal but only partial Faraday cages, a small percentage of the RF fieldstill is able to penetrate to the interior, however not enough to give areasonable visibility in the stent interior.

One approach to achieving the reasonable visibility would be to raisethe energy of the RF field to such high levels that enough energyremains after passing through the partial stent shield forvisualization. Unfortunately, taking this approach will cause the tissueof the body to be heated to unacceptable levels.

BRIEF DESCRIPTION OF THE DRAWINGS

The illustrations provided in the Figures are not to scale.

FIG. 1 illustrates an embodiment of a resonator device according to thepresent invention.

FIG. 2 illustrates an embodiment of a layered structure for a capacitorstructure according to the present invention.

FIG. 3 illustrates an embodiment of a resonator device according to thepresent invention.

FIG. 4 illustrates an embodiment of a resonator device according to thepresent invention.

FIG. 5 illustrates an embodiment of a resonator device according to thepresent invention.

FIG. 6 illustrates an embodiment of a resonator device according to thepresent invention.

FIG. 7 illustrates an embodiment of a system including a resonatordevice according to the present invention.

DETAILED DESCRIPTION

The figures herein follow a numbering convention in which the firstdigit or digits correspond to the drawing figure number and theremaining two (2) digits identify an element or component in thedrawing. Similar elements or components between different figures may beidentified by the use of similar digits. For example, 110 may referenceelement “10” in FIG. 1, and a similar element may be referenced as 210in FIG. 2. As will be appreciated, elements shown in the variousembodiments herein can be added, exchanged, and/or eliminated so as toprovide a number of additional embodiments. In addition, discussion offeatures and/or attributes for an element with respect to one figure canalso apply to the element shown in one or more additional figures.

Embodiments of the present invention are directed to medical deviceapparatus, systems, and methods of using the medical device. Generally,the medical device includes a resonator to be used in conjunction withan additional implantable medical device. These implantable medicaldevices include devices that traditionally have produced artifacts(signal loss) in images obtained by magnetic resonance imaging (MRI)systems. Embodiments of the present invention address the problem ofartifacts (signal loss) produced in magnetic resonance (MR) images inaddition to allowing for more complete MR images to possibly be obtainedfrom implantable medical devices.

Examples of such implantable medical devices include, but are notlimited to, stents and/or shunts as are used in dialysis, artificialveins, arteries and grafts, esophageal stenosis, esophageal cancer,esophageal varacies, lung bronchi for cancer treatment, urethra,hydrocephalus shunt elongate tubes, trachea, middle ear elongate tubes,lymphatic ducts and grafts, gastrointestinal stenosis and inflammatorydiseases (e.g. Crohn's disease), pyloric stenosis, implantable sensingdevices, intravascular blood pressure devices, and biliary atresia.Examples of other types of implantable medical devices are alsopossible.

Typically, artifacts in MR images are due in large part to distortionsin the magnetic field caused by the implanted medical device. Forexample, metallic stents can cause susceptibility and radiofrequencyartifacts in MR images that do not allow for complete visualization ofthe stent lumen by magnetic resonance angiography (MRA). This is due tosusceptibility artifacts and radiofrequency shielding of the metallicstents. Embodiments of the present invention can provide the potentialfor reduced artifacts during MR imaging with different MRA techniquesthrough the use of a resonator device in conjunction with a medicaldevice (e.g., metallic vascular stent).

In addition to allowing for more complete MR images to be obtained fromimplantable medical devices, embodiments of the present invention canalso allow for a more uniform amplification of a radio frequency (RF)magnetic field. An example of such an RF magnetic field includes thoseproduced and sensed by during MRA. Providing a more uniformamplification of an RF magnetic field in and/or around an implantedmedical device, such as a metallic stent, may allow for the resulting MRimages from within the implanted medical device to provide more detailedand meaningful MR images.

FIG. 1 illustrates one embodiment of a resonator device 100 of thepresent invention. The resonator device 100 is illustrated as having aninduction coil 102 and a conductive member 104 positioned adjacent eachother. In the present embodiment, the conductive member 104 is in theform of a vascular stent 106 that has an electrically conductive body.The resonator device 100 further includes a dielectric layer positionedbetween at least a portion of the induction coil 102 and the conductivemember 104 to form a capacitor structure 108. The induction coil 102 canbe electrically connected in series to the capacitor structure 108 toform the resonator device 100.

In various embodiments, the induction coil 102 can have a number ofconfigurations that are positioned at a variety of locations relativethe vascular stent 106. For example, as illustrated the induction coil102 can include a first end 110 and a second end 112. The induction coil102 can also include a first coil segment 114 and a second coil segment116. As illustrated, the first coil segment 114 can be positionedadjacent a first stent end 118, and the second coil segment 116 can bepositioned adjacent a second stent end 120. In one embodiment, the firstcoil segment 114 includes the first end 110 that is coupled to theelectrically conductive body of the vascular stent 106. In an additionalembodiment, the second coil segment 116 includes the second end 112 thatis coupled in series through the dielectric layer to form the capacitorstructure 108 of the resonator device 100.

In one embodiment, the windings of the first and second coil segments114, 116 are wound in a common direction 122. In addition, the first andsecond coil segments 114, 116 are at least electrically coupled throughthe use of a connection member 124. As used herein, a winding includesan electrically conductive wire wound one complete turn about a centerof the resonator device 100. In one embodiment, the connection member124 can extend over the vascular stent 106 either adjacent an exteriorsurface 126 or an interior surface 128 of the vascular stent 106. In analternative embodiment, the connection member 124 can be woven in andout of the vascular stent 106 structure.

In one embodiment, the connection member 124 can be constructed of thesame material as the induction coil 102. Alternatively, the connectionmember 124 can be constructed of a material that is different (e.g.,different conductivity, flexibility, malleability, stiffness) than thematerial used for the induction coil 102. In addition, the connectionmember 124 can have a number of different cross-sectional profiles,including but not limited to, circular, oval, triangular, and polygonal.The cross-sectional area of the connection member 124 can also begreater than or equal to that of the induction coil 102. For example,the connection member 124 could have a diameter that is greater than orequal to the diameter of the induction coil 102. In an alternativeembodiment, the cross-sectional area of the connection member 124 can beless than or equal to that of the induction coil 102.

As illustrated, the connection member 124 can be an elongate member thatpasses adjacent the exterior surface 126 of the vascular stent 106. Inan alternative embodiment, the connection member 124 can be in the formof a helix that extends along the resonator device 100. The connectionmember 124 can also be sheathed with an electrical insulator (e.g.,e-PTFE or pyrolene) to electrically insulate the induction coil 102 fromthe vascular stent 106 and or the induction coil 102. In addition, oneor more portions of the connection member 124 could be made radioopaque,as discussed herein.

In various embodiments, the vascular stent 106, the first coil segment114 and the connection member 124 can be formed from a single piece ofmaterial. For example, the vascular stent 106, the first coil segment114, and the connection member 124 could be cut (laser or water cut)from a single elongate tube of material. Alternatively, the vascularstent 106, the first coil segment 114 and the connection member 124could be formed from a single length of material (e.g., a length ofwire). The connection member 124 could then be connected to the secondcoil segment 116 of the induction coil 102. In one embodiment,connecting the connection member 124 to the second coil segment 116 canbe accomplished through a welding process, such as laser welding.

In an alternative embodiment, the vascular stent 106, the first andsecond coil segments 114, 116 and the connection member 124 can beformed from either a single piece of material or a single length ofmaterial, as discussed herein. For example, in one configuration asingle piece or length of material can be used to form, in order, thevascular stent 106, the first coil segment 114, the connection member124 and the second coil segment 116. From this configuration, theconnection member 124 would then be bent back over the windings of thefirst coil segment 110 to position the second coil segment 116 adjacentthe second stent end 120. The second end 112 of the induction coil 102can then be coupled through the dielectric layer to complete the circuitof the resonator device 100.

As illustrated in the present embodiment, the conductive member 104 isin the form of the vascular stent 106. The vascular stent 106 includes atubular shaped body 130 defined by elongate members 132 disposed betweenthe first and second end 118 and 120. The tubular shaped body 130 alsoincludes a surface defining at least a portion of a lumen 134 of theresonator device 100. In one embodiment, the elongate member 132 can beformed of a material which is electrically conductive. In addition, thematerial of the elongate member 132 also has the requisite strength andelasticity characteristics to permit the tubular shaped body 130 to beexpanded from the first cross-sectional size to the secondcross-sectional size. The material also allows the tubular shaped body130 to retain its expanded configuration with the second cross-sectionalsize. Examples of such materials include, but are not limited to,tantalum, magnesium, tungsten, niobium, stainless steel, titanium,memory metal alloys (such as Nitinol), or any suitable plastic materialhaving the requisite characteristics described herein.

The elongate member 132 can have a cylindrical cross-section, but aswill be appreciated the elongate member 132 could have othercross-sectional configurations, such as triangular, square, rectangular,and/or hexagonal, among others. In addition, the elongate member 132 canhave a non-uniform cross-sectional configuration along its length, suchas tapered, bell shaped, or changing from one cross-sectional shape(e.g., cylindrical) to a second cross-sectional shape (e.g., elliptical)in case of a bifurcation. As illustrated, the elongate member 132 can beconfigured as a continuous helix of connected spirals or loops having asinuous or zigzag configuration. The elongate member 132 can also befixedly secured to one another at predetermined intersection points andconnectors 136 so as to help resist radial collapse of the vascularstent 106 and to help maintain its second cross-sectional size.

In the embodiment illustrated in FIG. 1, the vascular stent 106 isconfigured to function as the capacitor structure 108. In variousembodiments, the vascular stent 106 has a layered configuration of theconductive member 104, a dielectric layer, and at least a portion of theinduction coil 102 that forms the capacitor structure 108. For example,in the present embodiment the elongate member 132 forming the vascularstent 106 provides the conductive member 104. The dielectric layer ispositioned over at least a portion of the elongate member 132, where theinduction coil 102 is electrically connected in series to form theresonator device 100.

In one embodiment, the elongate member 132 and the portion of theinduction coil 102 contacting the dielectric material form electricallyisolated (insulated) conductive surfaces for the capacitor structure108. In an additional embodiment, at least a portion of the elongatemember 132 can further include an electrically conductive coating overthe dielectric layer so as to increase the surface area of the capacitorstructure 108. In other words, the capacitor structure 108 can includethe elongate member 132 coated with the dielectric material, where theelectrically conductive coating is provided over the dielectric toprovide the capacitor structure 108. The second end 112 of the inductioncoil 102 can then be electrically coupled to the electrically conductivecoating to complete the circuit of the resonator device 100. Thecapacitor structure 108 and/or the induction coil 102 can also be coatedwith an electrical insulator (e.g., e-PTFE or pyrolene) to electricallyinsulate the capacitor structure 108 and/or the induction coil 102.

FIG. 2 provides an embodiment illustrating the layered structure of thecapacitor structure described herein. As illustrated, the capacitorstructure includes the elongate member 232 of the vascular stent thatprovides the conductive member 204. The dielectric layer 240 can bepositioned over at least a portion of the elongate member 232. Theelectrically conductive coating 242 can then be positioned over thedielectric layer 240 to form the capacitor structure 208.

FIG. 2 also illustrates an embodiment of the capacitor structure 208.For example, the elongate member 232 coated with the dielectric material240 and the electrically conductive coating 242 provides the capacitorstructure 208. The first end 210 of the induction coil 202 can beelectrically connected to the conductive member 204 and the second end212 of the induction coil 202 can be electrically coupled to theelectrically conductive coating 242 to complete the capacitor structure208 of the resonator device.

Possible dielectric materials include, but are not limited to, metaloxides such as tantalum oxide, aluminum oxide, niobium oxide,niobium-zirconium alloy oxide; ceramic and/or glasses such as alumina oraluminosilicates and borosilicate; minerals such as mica (an alkalimetal aluminosilicate, hydrate); polymers such as polyesters (e.g.,Mylar), polyamides (e.g., Nylon), polycarbonate, polyetheretherketones(PEEK), poly(phenylene oxide), poly(phenylene sulfide), poly(vinylchloride), poly(chlorotrifluoroethylene), poly(p-phenyleneethylene),polystyrene, polyethylene, polypropylene, and poly(tetrafluoroethylene).Other dielectric materials are also possible.

As will be appreciated, the dielectric layer and/or the electricallyconductive coating can be formed as a film deposited on the elongatemember 132 through a number of different surface coating techniques.Examples of such coating techniques include, but are not limited to,chemical or physical deposition techniques. Example of these respectivetechniques include, but are not limited to, solution casting, ink-jetdeposition, aerosol deposition, dip coating, spin coating, plasmapolymerization, electrochemical polymerization, catalyticpolymerization, photo-activatable polymerization, molecular-aggregation,vacuum sublimation, plasma deposition, pulse-laser deposition (PLD),matrix assisted pulsed-laser evaporation, chemical vapor deposition(CVD), plasma assisted CVD, thin film growth, sputtering, evaporation(thermal and e-beam), ion vapor deposition, and laser and/or electronbeam assisted processing (e.g., laser ablation processing).

In one embodiment, the dielectric layer of the capacitor structure 108can have a dielectric constant that changes in a predetermined fashionbetween at least a portion of the induction coil 102 and the conductivemember 104. In the various embodiments, configuring the changes in thedielectric constant along the capacitor structure 108 can allow for amore uniform current distribution to result in the resonator device 100.

Examples of such configurations include, but are not limited to, thedielectric layer having two or more sections that each has a dielectricconstant that is different than the dielectric constant of othersections of the dielectric layer. This configuration can provide for achange in the capacitance value of the capacitor structure 108 betweenthe first end 110 and the second end 112 of the induction coil 102. Forexample, the value of the dielectric constant for the two or moresections can increase between the first end 110 and the second end 112of the induction coil 102 to change the capacitance value of thecapacitor structure 108. In an additional embodiment, the dielectriclayer can have a thickness that increases along the conductive member104 of the vascular stent 106 between the first end 110 and the secondend 112 of the induction coil 102 to change the capacitance value of thecapacitor structure 108.

As illustrated in the present embodiment, the induction coil 102 extendsfrom the first end 118 to the second end 120 of the stent 106. Invarious embodiments, the induction coil 102 can be configured to extendover at least a portion of the exterior surface 126 of the vascularstent 106. For example, a portion of the induction coil 102 can extendover the exterior surface 126 of one or both of the first and/or secondends 118, 120 of the vascular stent 106. In an additional embodiment, aportion of the induction coil 102 can extend over the interior surface128 of one or both of the first and/or second ends 118, 120 of thevascular stent 106. Different combinations are also possible (e.g., oneportion of the induction coil 102 extends over the exterior surface 126at the first end 118 while a second portion of the induction coil 102extends over the interior surface 128 at the second end 120).

As illustrated, the induction coil 102 includes an elongateconfiguration having windings that extend circumferentially in a helicalstructure as illustrated. In one embodiment, windings of the helicalstructure can be equally spaced from each other. In an alternativeembodiment, windings of the helical structure can have a predeterminednon-consistent spacing relative to each other along the helicalstructure. In one embodiment, this non-consistent spacing can allow fordifferences in the winding density (number of windings per meter) alongthe length of the induction coil 102.

In one embodiment, the induction coil 102 can extend continuously downthe length of the resonator device 100 (i.e., the induction coil 102does not deviate along the length of the resonator device 100).Alternatively, the induction coil 102 can include a “zigzag”configuration as the induction coil 102 extends down the length ofresonator device 100. As will be appreciated, other shapes andconfigurations that can act as an induction coil, besides helical coils,are also possible.

The induction coil 102 can be formed of one or more conductive members(e.g., two or more members in parallel). In addition, differentcross-sectional geometries can be used for the induction coil 102. Forexample, the cross-sectional geometries can include circularrectangular, oval and/or polygonal, among others. Other shapes are alsopossible.

The conductive members of the induction coil 102 can also have a numberof different sizes and structural configurations. For example, theconductive members can have a size and a shape sufficient to maintain apredetermined shape of the induction coil 102 in its deployed state.Alternatively, the size and the shape of each of the induction coil 102can be supported by a structural support, as discussed in co-pendingU.S. patent application entitled “Resonator for Medical Device”, docketnumber 05-0048US, U.S. patent application Ser. No. 11/207,304, can beconfigured to maintain the predetermined shape of the induction coil 102in its deployed state.

In one embodiment, the conductive members of the induction coil 102 canbe a metal or metal alloy. Examples of such metals and metal alloysinclude, but are not limited to, platinum, titanium, niobium, and memorymetals alloys such as Nitinol, titanium-palladium-nickel,nickel-titanium-copper, gold-cadmium, iron-zinc-copper-aluminum,titanium-niobium-aluminum, hafnium-titanium-nickel,iron-manganese-silicon, nickel-titanium, nickel-iron-zinc-aluminum,copper-aluminum-iron, titanium-niobium, zirconium-copper-zinc, andnickel-zirconium-titanium. Other metal and metal alloys are alsopossible. Further examples include polymeric wires provided with noblemetal (e.g., gold) sputter coat, such as polyamide 12, polyethylene, andpolycarbonate sputter coated with gold.

In addition, one or more of the components of the resonator device 100can be made radioopaque. For example, one or more portions of theinduction coil 102 could be clad with a radioopaque material to make theresonator device 100 radioopaque. Alternatively, one or more discreteradioopaque markers having a predetermined shape can be added topredetermined portions of the resonator device 100. Example of suitablematerials for the radioopaque markers include, but are not limited to,copper, tungsten, gold, silver, platinum and alloys thereof.

The induction coil 102 can further include spacers 144 positionedbetween the windings of the induction coils 102. In one embodiment, thespacers 144 provide for electrical insulation, structural support, andstructural spacing for adjacent windings of the coil 102. Spacers 144can be coupled to the induction coil 102 in a number of ways. Forexample, a pair of spacers 144 could be sandwiched around the inductioncoil 102 and bonded with heat and/or chemical adhesive. Spacers 144could be wound, twisted and/or braided around each other and theinduction coil 102. The spacers 144 could then be bonded with heatand/or chemical adhesive.

Examples of suitable materials for the spacers 144 include, but are notlimited to non-biodegradable and/or biodegradable materials. Examples ofnon-biodegradable materials include, but are not limited to, ceramic,polystyrene; polyisobutylene copolymers and styrene-isobutylene-styreneblock copolymers such as styrene-isobutylene-styrene tert-blockcopolymers (SIBS); polyvinylpyrrolidone including cross-linkedpolyvinylpyrrolidone; polyvinyl alcohols, copolymers of vinyl monomerssuch as EVA; polyvinyl ethers; polyvinyl aromatics; polyethylene oxides;polyesters including polyether sulfone; polyalkylenes includingpolypropylene, polyethylene and high molecular weight polyethylene;polyurethanes; polycarbonates, silicones; siloxane polymers; cellulosicpolymers such as cellulose acetate; polymer dispersions such aspolyurethane dispersons (BAYHDROL); squalene emulsions; and mixtures andcopolymers of any of the foregoing.

Examples of biodegradable materials include, but are not limited to,polycarboxylic acid, polylacetic acid, polyhydroxybuterate,polyanhydrides including maleic anhydride polymers; polyorthoesters;poly-amino acids; polyethylene oxide; polyphosphazenes; polyacetic acid,polyglycolic acid and copolymers and copolymers and mixtures thereofsuch as poly(L-lacetic acid) (PLLA), poly (D,L,-lactide), poly(laceticacid-co-glycolic acid), 50/50 (DL-lactide-co-glycolide); polydioxanone;polypropylene fumarate; polydepsipeptides; polycaprolactone andco-polymers and mixtures thereof such aspoly(D,L-lactide-co-caprolactone) and polycaprolactone co-butylacrylate;polyhydroxybutyrate valerate and blends; polycarbonates such astyrosine-derived polycarbonates and arylates, polyiminocaronates, andpolydimethyltrimethylcarbonates; cyanoacrylate; calcium phosphates;polyglycosaminoglycans; macromolecules such as polysaccharides(including hyaluronic acid, cellulose, and hydroxypropylmethylcellulose; gelatin; starches; dextrans; alginates and derivativesthereof), proteins and polypeptides; and mixtures and copolymers of anyof the foregoing. The biodegradable polymer may also be a surfaceerodable polymer such as polyhydroxybutyrate and its copolymers,polycaprolactone, polyanhydrides (both crystalline and amorphous),maleic anhydride copolymers, and zinc-calcium phosphate.

The spacers 144 can further include one or more therapeutic agents. Inone embodiment, the one or more therapeutic agents can be integratedinto the material matrix of and/or coated on the surface of the spacers144. The one or more therapeutic agents can then leach and/or bereleased from the spacers 144 once implanted.

Examples of therapeutic agents include, but are not limited to,pharmaceutically acceptable agents such as non-genetic therapeuticagents, a biomolecule, a small molecule, or cells. Exemplary non-genetictherapeutic agents include anti-thrombogenic agents such as heparin,heparin derivatives, prostaglandin (including micellar prostaglandinE1), urokinase, and PPack (dextrophyenylalanine proline argininechloromethylketone); anti-proliferative agents such as enoxaprin,angiopenptin, sirolimus (rapamycin), tacrolimus, everolimus monoclonalantibodies capable of blocking smooth muscle cell proliferation,hirudin, and acetylsalicylic acid; anti-inflammatory agents such asdexamethasone, rosiglitazone, prenisolone, corticosterone, budesonide,estrogen, estrodiol, sulfasalazine, acetylsalicylic acid, mycophenolicacid, and mesalamine; anti-neoplastic/anti-proliferative/anti-mitoticagents such as paclitaxel, epothilone, cladribine, 5-fluorouracil,methotrexate, doxorubicin, daunorubicin, cyclosporine, cisplatin,vinblastine, vincristine, epothilones, endostatin, trapidil,halofuginone, and angiostatin; anti-cancer agents such as antisenseinhibitors of c-myc oncogene; anti-microbial agents such as triclosan,cephalosporins, aminoglycosides, nitrofurantoin, silver ions, compounds,or salts; biofilm synthesis inhibitors such as non-steroidalanti-inflammatory agents and chelating agents such asethylenediaminetetraacetic acid,O,O′-bis(2-aminoethyl)ethyleneglycol-N,N,N′,N′-tetraacetic acid andmixtures thereof; antibiotics such as gentamycin rifampin, minocyclin,and ciprofolxacin; antibodies including chimeric antibodies and antibodyfragments; anesthetic agents such as lidocaine, bupivacaine, andropivacaine; nitric oxide; nitric oxide (NO) donors such as lisidomine,molsidomine, L-arginine, NO-carbohydrate adducts, polymeric oroligomeric NO adducts; anti-coagulants such as D-Phe-Pro-Argchloromethyl ketone, an RGD peptide-containing compound, heparin,antithrombin compounds, platelet receptor antagonists, anti-thrombinantibodies, anti-platelet receptor antibodies, enoxaparin, hirudin,warfarin sodium, Dicumarol, aspirin, prostaglandin inhibitors, plateletaggregation inhibitors such as cilostazol and tick antiplatelet factors;vascular cell growth promotors such as growth factors, transcriptionalactivators, and translational promotors; vascular cell growth inhibitorssuch as growth factor inhibitors, growth factor receptor antagonists,transcriptional repressors, translational repressors, replicationinhibitors, inhibitory antibodies, antibodies directed against growthfactors, bifunctional molecules consisting of a growth factor and acytotoxin, bifunctional molecules consisting of an antibody and acytotoxin; cholesterol-lowering agents; vasodilating agents; agentswhich interfere with endogeneus vascoactive mechanisms; inhibitors ofheat shock proteins such as geldanamycin; and any combinations andprodrugs of the above.

Exemplary biomolecules includes peptides, polypeptides and proteins;oligonucleotides; nucleic acids such as double or single stranded DNA(including naked and cDNA), RNA, antisense nucleic acids such asantisense DNA and RNA, small interfering RNA (siRNA), and riobozymes;genes; carbohydrates; angiogenic factors including growth factors; cellcycle inhibitors; and anti-restenosis agents. Nucleic acids may beincorporated into delivery systems such as, for example, vectors(including viral vectors), plasmids or liposomes.

Non-limiting examples of proteins include monocyte chemoattractantproteins (“MCP-1) and bone morphogenic proteins (“BMP's”), such as, forexample, BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 (Vgr-1), BMP-7 (OP-1), BMP-8,BMP-9, BMP-10, BMP-11, BMP-12, BMP-13, BMP-14, BMP-15. These BMPs can beprovided as homodimers, heterodimers, or combinations thereof, alone ortogether with other molecules. Alternatively, or in addition, moleculescapable of inducing an upstream or downstream effect of a BMP can beprovided. Such molecules include any of the “hedghog” proteins, or theDNA's encoding them. Non-limiting examples of genes include survivalgenes that protect against cell death, such as anti-apoptotic Bcl-2family factors and Akt kinase and combinations thereof. Non-limitingexamples of angiogenic factors include acidic and basic fibroblastgrowth factors, vascular endothelial growth factor, epidermal growthfactor, transforming growth factor α and β, platelet-derived endothelialgrowth factor, platelet-derived growth factor, tumor necrosis factor α,hepatocyte growth factor, and insulin like growth factor. A non-linearexample of a cell cycle inhibitor is a cathespin D (CD) inhibitor.Non-limiting examples of anti-restenosis agents include p15, p16, p18,p19, p21, p27, p53, p57, Rb, nFkB and E2F decoys, thymidine kinase(“TK”) and combinations thereof and other agents useful for interferingwith cell proliferation.

Exemplary small molecules include hormones, nucleotides, amino acids,sugars, and lipids and compounds have a molecular weight of less than100 kD.

Exemplary cells include stem cells, progenitor cells, endothelial cells,adult cardiomyocytes, and smooth muscle cells. Cells can be of humanorigin (autologous or allogenic) or from an animal source (xenogenic),or genetically engineered. Non-limiting examples of cells include sidepopulation (SP) cells, lineage negative (Lin-) cells includingLin-CD34−, Lin-CD34+, Lin-cKit+, mesenchymal stem cells includingmesenchymal stem cells with 5-aza, cord blood cells, cardiac or othertissue derived stem cells, whole bone marrow, bone marrow mononuclearcells, endothelial progenitor cells, skeletal myoblasts or satellitecells, muscle derived cells, go cells, endothelial cells, adultcardiomyocytes, fibroblasts, smooth muscle cells, adult cardiacfibroblasts +5-aza, genetically modified cells, tissue engineeredgrafts, MyoD scar fibroblasts, pacing cells, embryonic stem cell clones,embryonic stem cells, fetal or neonatal cells, immunologically maskedcells, and teratoma derived cells.

The therapeutic agents may be combined to the extent such combination isbiologically compatible.

The induction coil 102 and the vascular stent 106 are configured toallow the lumen 134 of the resonator device 100 to expand from a firstcross-sectional size in an un-deployed state to a second cross-sectionalsize in a deployed state. This allows the resonator device 100 to beintroduced into a body with the first cross-sectional size and then beexpanded to the second cross-sectional size at the predeterminedlocation within the body. For example, the resonator device 100 can bepositioned over a balloon of a balloon catheter in its firstcross-sectional size (e.g., its un-deployed configuration). The ballooncan then be inflated to expand the resonator device 100 to its secondcross-sectional size (e.g., its deployed configuration). Alternatively,when the induction coil 102 and vascular stent 106 are formed of amemory metal alloy (such as Nitinol), the resonator device 100 can beintroduced into the body in its first cross-sectional size (e.g., itsun-deployed configuration) and then released to expand the resonatordevice 100 to its second cross-sectional size (e.g., its deployedconfiguration).

In one embodiment, the diameter of lumen 134 can be essentially equalalong the length of the resonator device 100. In an alternativeembodiment, the expandable diameter of the lumen 134 can change alongthe length of the resonator device 100. For example, the diameter of thelumen 134 can increase or decrease along the length of the resonatordevice 100. Alternatively, the diameter of the lumen 134 can increasealong the length of the resonator device 100 to a predetermined pointand then decrease again. Other configurations are also possible.

As will be appreciated, the induction coil 102 includes windings ofelectrically conductive material that in conjunction with the capacitorstructure 108 can be used to tune the resonator device 100 to apredetermined radio frequency (RF). Examples of parameters used intuning the resonator device 100 include, but are not limited to, thenumber of windings and the cross sectional area of the induction coil102. In one embodiment, the number of windings can be modified based onthe configuration of induction coil 102. Parameters of the capacitorstructure 108 can also be used in the tuning the resonator device 100.

FIG. 3 illustrates an additional embodiment of the resonator device 300of the present invention. As illustrated, the resonator device 300 is inthe form of a vascular stent 306, as discussed generally herein. Theresonator device 300 includes the elongate members 332 of the stent 306that provide both the mechanical strength to support a vessel and theconduction member 304 for the capacitor structure 308. The resonatordevice 300 further includes both the induction coil 302 and thecapacitor structure 308 that overly the conduction member 304 of thevascular stent 306 to form the resonator device 300. In other words, theresonator device 300 is integrated into the vascular stent 306. Asdiscussed herein, the resulting resonator device 300 can resonate at themagnetic resonant frequency as used by the RF generator within the MRIsystem.

By way of example, the layers forming the induction coil 302 and thedielectric layer are located over predetermined portions of theconduction member 304 so as to provide the induction coil 302 andcapacitor structure 308. In one embodiment, the layers forming theinduction coil 302 and the capacitor structure 308 are applied to orformed upon the exterior surface 326 of the vascular stent 306. Anexample of such a structure is provided in U.S. Pat. No. 6,767,360 toAlt et al., which is incorporated herein by reference in its entirety.

As illustrated in FIG. 3, the induction coil 302 has a predeterminedpattern on the exterior surface 326 of the vascular stent 306. Thecapacitor structure 308 can further be formed between the induction coil302 and the elongate member 332 of the vascular stent 306. In oneembodiment, this can be achieved by depositing (or otherwise creating)the dielectric layer on the exterior surface 326 of the vascular stent306 in a circumferential pattern that extends along the vascular stent306. In one embodiment, the circumferential pattern extending along thevascular stent 306 corresponds to the configuration of the inductioncoil 302. The electrically conductive material forming the inductioncoil 302 can then be deposited (or created) over the dielectric layer soas to complete the resonator circuit 300.

In one embodiment, the dielectric layer of the capacitor structure 308can have a dielectric constant that changes, as discussed herein, in apredetermined fashion between at least a portion of the induction coil302 and the conductive member 304. For example, the dielectric layer caninclude two or more sections that each has a dielectric constant that isdifferent than the dielectric constant of other sections of thedielectric layer. This configuration can provide for a change in thecapacitance value of the capacitor structure 308 between the first end310 and the second end 312 of the induction coil 302, as discussedherein. In an additional embodiment, the dielectric layer can have athickness that increases along the conductive member 304 of the vascularstent 306 between the first end 310 and the second end 312 of theinduction coil 302 to change the capacitance value of the capacitorstructure 308.

FIG. 4 provides an additional embodiment of the resonator device 400that includes the induction coil 402, a conductive film 450 positionedadjacent the induction coil 402, and a dielectric layer 440. Asillustrated, the dielectric layer 440 can be positioned between at leasta portion of the induction coil 402 and the conductive film 450 to formthe capacitor structure 408. As will be discussed herein, the dielectriclayer 440 can be in the form of a flexible elongate body on which theinduction coil 402 and conductive film 450 are positioned.

As illustrated in FIG. 4, the dielectric layer 440 is configured as anelongate tube 452 having a first end 454 and a second end 456. Theelongate tube 452 includes a first surface 458 and a second surface 460opposite the first surface 458. In one embodiment, the conductive film450 can be located on at least a portion of the first surface 458 andthe second surface 460. For example, the conductive film 450 on thesecond surface 460 can be at least partially contiguous with theconductive film 450 on the first surface 458 adjacent the first end 454,and the conductive film 450 on the second surface 460 can be separatedfrom the conductive film 450 on the first surface 458 adjacent thesecond end 456.

As illustrated, the induction coil 402 can be located on the secondsurface 460 where the first end 410 of the induction coil 402 can beelectrically coupled to the conductive film 450 adjacent the first end454 of the elongate tube 452. The second end 412 of the induction coil402 can be electrically coupled to the conductive film 450 adjacent thesecond end 456 of the elongate tube 452. In one embodiment, this allowsfor the elongate tube 452 to form the dielectric layer 440 to completethe circuit of the resonator device 400. In an additional embodiment,the resonator device 400 can further include a resistor 464 in serieswith the induction coil 402, the conductive film 450 and the capacitorstructure 408. In one embodiment, use of the resistor 464 can allow fora wider frequency response of the resonator device 400 as compared todevices without such a resistor 464.

As illustrated, the conductive film 450 extends longitudinally along thefirst surface 458 of the elongate tube 450. In addition, the conductivefilm 450 defines a gap 462 that extends longitudinally along the firstsurface 458 of the elongate tube 452. In one embodiment the gap 462provides for a break in the film 450 so as to prevent the conductivefilm 450 from interfering with received and amplified RF signals fromthe resonator device 400. As will be appreciated, changes in the surfacearea of film 450, and the induction coil 402, along with the choice ofdielectric material can influence the operating parameters of thecapacitor structure 408.

In one embodiment, the dielectric layer 440 configured as the elongatetube 452 can be formed by an extrusion process. Alternatively, theelongate tube 452 structure of the dielectric layer 440 can be formed bya weaving or knitting process using one or more filaments, ormulti-filament yarn, of the dielectric material as described herein.Examples of suitable dielectric materials for use as the elongate tube452 and/or use on the elongate tube 452 include, but are not limited to,those described herein. In addition, the elongate tube 452 can beformed, at least partially, of a biodegradable material, as are providedherein. As will be appreciated, the dielectric layer 440 may also becoated with one or more therapeutic agents, proteins, biomolecules,anticoagulant, anti-inflammatory, pro-endothelization compounds, amongothers, as described herein.

In one embodiment, the conductive film 450 and the induction coil 402can be formed from an electrically conducive thin film as positioned onthe elongate tube 452. Forming the conductive film 450 and the inductioncoil 402 as a thin conductive film can be accomplished in a number ofways. For example, the conductive film 450 and the induction coil 402can be formed using either chemical or physical deposition techniques.Example of these techniques include, but are not limited to, chemicalvapor deposition (CVD), plasma assisted CVD, thin film growth,sputtering, evaporation (thermal and e-beam), ion vapor deposition, andlaser and/or electron beam assisted processing (e.g., laser ablationprocessing).

As will be appreciated, the conductive film 450 and the induction coil402 can have a thickness sufficient to conduct the energy through theresonator device 400. In addition, the induction coil 402 and/or theconductive film 450 can be formed of conductive nanoparticles. As usedherein, a nanoparticle is a microscopic particle whose size is measuredin nanometers. Examples of suitable nanoparticles include those that canbe oxidized, including but not limited to gold (Au). In one embodiment,this allows for the induction coil 402 and/or the conductive film 450formed of the nanoparticles to be biodegradable.

In various embodiments, the conductive film 450 having the gap 462 canfirst be formed on the elongate tube 452, where the second surface 460is initially defines the outside surface of the tube 452. In oneembodiment, the conductive film 450 with the gap 462 is formed on thesecond surface 460 of elongate tube 452. As the conductive film 450 isformed a portion of the material forming the film covers the first andsecond end 454, 456 and a portion of the first surface 458 thatinitially defines the lumen of the tube 452. The wall of the tube 452can then be inverted so that the first surface 458 defines the outsidesurface and the second surface 460 defines the lumen of the tube 452.

The induction coil 402 can then be formed on the first surface 458,where the first end 410 of the induction coil 402 can be electricallycoupled to the conductive film 450 adjacent the first end 454 of theelongate tube 452. The second end 412 of the induction coil 402 can beelectrically coupled to the conductive film 450 adjacent the second end456 of the elongate tube 452. Conductive film 450 on the second end 456can then be removed so as to allow the elongate tube 452 to form thedielectric layer 440 to complete the circuit of the resonator device400.

As discussed herein, stents and other metallic implants can causepartial shielding of a RF field by the Faraday Effect. As a result, ithas been difficult to obtain MRI visibility inside an implant. In aneffort to obtain a better MRI visibility the implant can be positionedinside of the RF field of a local (implanted) resonating circuit, asdiscussed herein, that is tuned to the RF-frequency of the MRI system.The resonator-coil will cause the RF-field (as sent out by the MRI coil)to be magnified inside the coil. The result is to raise the energy levelat the position of the implant without heating other parts of the body.

Embodiments of the resonator device 400 can be used in association, orin conjunction, with a vascular stent or other medical device. Forexample, the resonator device can be provided partially over at least apart of the vascular stent. In another example, the resonator device 400can be provided partially within at least a part of the vascular stent.The resonator device 400 in conjunction with the vascular stent can thenoperate in the presence of an electromagnetic field produced by an MRIsystem to reduce the artifacting (signal loss) in images obtained by anMRI system.

FIG. 5 provides an additional embodiment of the resonator device 500that includes the induction coil 502, the conductive film 550 positionedadjacent the induction coil 502, and the dielectric layer 540. Asillustrated, the dielectric layer 540 can be positioned between at leasta portion of the induction coil 502 and the conductive film 550 to formthe capacitor structure 508. As discussed herein, the dielectric layer540 is in the form of the elongate tube 552 having the first end 554 andthe second end 556.

The elongate tube 552 of the present embodiment further includes a firstexpandable support member 566 adjacent the first end 554 and a secondexpandable support member 568 adjacent the second end 556. In oneembodiment, the first and second expandable support members 566, 568 areelectrically isolated from the induction coil 502. As illustrated, thefirst and second expandable support members 566, 568 can at leastpartially encircle the elongate tube 552. In one embodiment, the firstand second expandable support members 566, 568 can include one or morerings that fully encircle the elongate tube 552. In an alternativeembodiment, the first and second expandable support members 566, 568 arepartial rings that either do not fully encircle the elongate tube 552 orhave a helical configuration in which each respective support member566, 568 does not form a closed and connected loop (i.e., the first andsecond expandable support members 566, 568 have a first and a second endthat are uncoupled).

The first and second expandable support members 566, 568 are configuredto change shape from a first diameter that permits intraluminal deliveryof the resonator device 500 into a body passageway, e.g., a lumen of thevasculature, to a second diameter that is larger than the firstdiameter. In one embodiment, the first and second expandable supportmembers 566, 568 can have a sinuous or a zigzag pattern that encirclesthe elongate tube 552. As will be appreciated, this type ofconfiguration allows the first and second expandable support members566, 568 to be expanded from their first diameter to the seconddiameter.

The first and second expandable support members 566, 568 can be formedof a material which has the requisite strength and elasticitycharacteristics to permit the support members to be expanded from thefirst diameter to the second diameter. The material also allows thefirst and second expandable support members 566, 568 to retain theirexpanded configuration with the second diameter. Examples of suchmaterials include, but are not limited to, tantalum, stainless steel,titanium, memory metal alloys (such as Nitinol), or any suitable plasticmaterial having the requisite characteristics described herein.

In one embodiment, the first and second expandable support members 566,568 help to secure the resonator device 500 at a predetermined positionwithin a patient. For example, the resonator device 500 could bepositioned upon a deflated balloon of a balloon catheter system. Uponpositioning the resonator device 500 at a predetermined location withinthe patients, the resonator device 500 could be implanted by inflatingthe balloon to expand the first and second expandable support members566, 568 so as to engage the resonator device 500 at the implant site.In an alternative embodiment, the first and second expandable supportmembers 566, 568 can be self-expanding, where the catheter deliverysystem would constrain the first and second expandable support members566, 568 in their first diameter until they were released at the implantsite.

FIG. 5 also illustrates an additional embodiment for a configuration ofthe induction coil 502. As illustrated, the induction coil 502 includesa helical configuration with a pitch that transitions from a firstpredetermined value 570 to a second predetermined value 572 as theinduction coil 502 extends longitudinally from the first end 510 of theinduction coil 502. In one embodiment, the second predetermined value572 occurs between the first end 510 and the second end 512 of theinduction coil 502. In addition, the pitch of the induction coil 502transitions from the second predetermined value 572 back to the firstpredetermined value 570 as the induction coil 502 extends longitudinallytoward the second end 512 of the induction coil 502. In one embodiment,imparting the pitch to the induction coil 502 as illustrated anddescribed herein can allow the resonator device 500 to receive andamplify RF signals impinging on the resonator device 500 from a greatervariety of angles.

FIG. 6 provides an additional embodiment of the resonator device 600 forimplanting in a body. The resonator device 600 includes the inductioncoil 602 having a first end 610 and a second end 612, as discussedherein. The resonator device 600 also includes a capacitor structure 608in series with the induction coil 602, as discussed herein. As will beappreciated, other capacitor structures besides those described hereinare also possible. Examples include plate capacitors and fractalcapacitors.

In various embodiments, the induction coil 602 can further include afirst density 674 and a second density of windings per meter for theinduction coil 602 configured so as to allow for a uniform currentdistribution in the resonator device 600. For example, the inductioncoil 602 can include the first density 674 of windings per meteradjacent the first and second ends 610, 612 and the second density 676of windings per meter between the first and second ends 610, 612. In oneembodiment, the first density 674 of windings per meter is greater thanthe second density 676 of windings per meter.

In the embodiment of FIG. 6, the induction coil 602 and the capacitorstructure 608 can be associated with a non-conductive elongate tube 678.In one embodiment, the non-conductive elongate tube 678 can be formed byan extrusion process. Alternatively, the non-conductive elongate tube678 can be formed by a weaving or knitting process using one or morefilaments, or multi-filament yarn, of the material as described herein.

Examples of suitable materials for use as the non-conductive elongatetube 678 include, but are not limited to, those described herein. Inaddition, the non-conductive elongate tube 678 can be formed, at leastpartially, of a biodegradable material, as are provided herein. As willbe appreciated, the non-conductive elongate tube 678 may also be coatedwith one or more therapeutic agents, proteins, biomolecules,anticoagulant, anti-inflammatory, pro-endothelization compounds, amongothers, as described herein.

In one embodiment, examples of the non-conductive elongate tube can befound in co-pending U.S. patent application Ser. No. ______, entitle“Resonator for Medical Device” to Weber et al., (Dkt. #s 05-0048US and202.0100001), which is hereby incorporated herein by reference in itsentirety. This co-pending application provides embodiments of astructural support in the form of a tube that supports an induction coiland a capacitor for a resonator device. In various embodiments, thenon-conductive elongate tube 678 can encase the induction coil 602and/or the capacitor structure 608 of the resonator device 600. In analternative embodiment, the non-conductive elongate tube 678 includes aperipheral surface on which the induction coil 602 is positioned.

Embodiments of the resonator device 600 can be used in association, orin conjunction, with a vascular stent or other medical device. Forexample, the resonator device can be provided over at least a part ofthe vascular stent. In another example, the resonator device 600 can beprovided within at least a part of the vascular stent. The resonatordevice 600 in conjunction with the vascular stent can then operate inthe presence of an electromagnetic field produced by an MRI system toreduce the artifacting (signal loss) in images obtained by an MRIsystem.

FIG. 7 illustrates a system having a catheter 780 with an elongate body782, an inflatable balloon 784 positioned adjacent a distal end 786, anda lumen 788 longitudinally extending in the elongate body 782 of thecatheter 780 from the inflatable balloon 784 to a proximal end 790. Inthe present example, the inflatable balloon 784 can be at leastpartially positioned within the lumen 792 of the resonator device 700.

The catheter 780 can further include a guidewire lumen 794 to receive aguidewire 796. Guidewire 796 and guidewire lumen 794 assist inpositioning the resonator device 700, as discussed herein, at apredetermined location within the body. Once in position, the inflatableballoon 784 can be inflated through the use of an inflation pump 798that can releasably couple to the lumen 788. As the inflatable balloon784 inflates, the resonator device 700 expands to the second diameter,as discussed herein, so as to position the resonator device 700 in thepatient. As will be appreciated, lumen 788 and 794 can be eccentric, asillustrated, or concentric.

While the present invention has been shown and described in detailabove, it will be clear to the person skilled in the art that changesand modifications may be made without departing from the scope of theinvention. As such, that which is set forth in the foregoing descriptionand accompanying drawings is offered by way of illustration only and notas a limitation. The actual scope of the invention is intended to bedefined by the following claims, along with the full range ofequivalents to which such claims are entitled.

In addition, one of ordinary skill in the art will appreciate uponreading and understanding this disclosure that other variations for theinvention described herein can be included within the scope of thepresent invention. For example, the resonator device can be coated witha non-thrombogenic biocompatible material, as are known or will beknown, one or more pharmaceuticals and/or biological compounds ormolecules.

Embodiments and illustrations described herein can further be modifiedand/or added to according to co-pending U.S. patent application Ser. No.09/779,204, entitled “Vascular Stent with Composite Structure forMagnetic Reasonance Imaging Capabilities” [sic], which is incorporatedherein by reference in its entirety.

In the foregoing Detailed Description, various features are groupedtogether in several embodiments for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the embodiments of the invention requiremore features than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus, the following claimsare hereby incorporated into the Detailed Description, with each claimstanding on its own as a separate embodiment.

1. A resonator device, comprising: an induction coil; a conductive filmpositioned adjacent the induction coil; and a dielectric layerconfigured as a flexible elongate tube having a first surface and asecond surface opposite the first surface, the flexible elongate tubebetween the induction coil and the conductive film to form a capacitorstructure.
 2. The resonator device of claim 1, where the conductive filmis on at least a portion of the first surface and the second surface ofthe flexible elongate tube and the induction coil is on the secondsurface of the flexible elongate tube.
 3. The resonator device of claim1, where the elongate tube has a first end and a second end, theconductive film on the second surface being at least partiallycontiguous with the conductive film on the first surface adjacent thefirst end, and the conductive film on the second surface being separatedfrom the conductive film on the first surface adjacent the second end.4. The resonator device of claim 1, where the induction coil includes afirst end and a second end, the first end electrically coupled to theconductive film adjacent the first end of the elongate tube, and thesecond end electrically coupled to the conductive film adjacent thesecond end of the elongate tube.
 5. The resonator device of claim 1,where the conductive film extends longitudinally along the first surfaceof the elongate tube.
 6. The resonator device of claim 5, where theconductive film defines a gap that extends longitudinally along thefirst surface of the elongate tube.
 7. The resonator device of claim 1,where the elongate tube includes a first end and a second end, theelongate tube having a first expandable support member adjacent thefirst end and a second expandable support member adjacent the secondend, where the first and second expandable support members areelectrically isolated from the induction coil.
 8. The resonator deviceof claim 1, where the elongate tube is formed of a biodegradablepolymer.
 9. The resonator device of claim 1, where conductivenanoparticles form the induction coil.
 10. The resonator device of claim1, including a resistor in series with the induction coil, theconductive film and the capacitor structure.
 11. A resonator device,comprising: an induction coil having a helical configuration with apitch that transitions from a first predetermined value to a secondpredetermined value as the induction coil extends longitudinally from afirst end of the induction coil; a conductive film positioned adjacentthe induction coil; and a dielectric layer between at least a portion ofthe induction coil and the conductive film to form a capacitorstructure, where the dielectric layer includes a flexible elongate body.12. The resonator device of claim 11, where the induction coil includesa second end, where the second predetermined value occurs between thefirst end and the second end of the induction coil.
 13. The resonatordevice of claim 12, where the pitch of the induction coil transitionsfrom the second predetermined value back to the first predeterminedvalue as the induction coil extends longitudinally toward a second endof the induction coil.
 14. The resonator device of claim 11, where adielectric layer configured as a flexible elongate tube having a firstsurface and a second surface opposite the first surface, the flexibleelongate tube between the induction coil and the conductive film to forma capacitor structure.
 15. The resonator device of claim 11, where thedielectric layer is configured as a elongate tube having a first surfaceand a second surface opposite the first surface, the conductive film onat least a portion of the first surface and the second surface and theinduction coil on the second surface.
 16. A vascular stent, comprising:elongate members, where the elongate members are electricallyconductive; an induction coil adjacent the elongate members; and adielectric layer between the elongate members and the induction coil toform a capacitor structure integral with the vascular stent.
 17. Thevascular stent of claim 16, where the dielectric layer is deposited onthe elongate members in a circumferential pattern that corresponds tothe configuration of the induction coil and extends along the vascularstent.
 18. The vascular stent of claim 16, where the dielectric layerhas a dielectric constant that changes in a predetermined fashionbetween at least a portion of the induction coil and the elongatemember.
 19. The vascular stent of claim 18, where the dielectric layerincludes two or more sections each having a dielectric constant that isdifferent than the dielectric constant of other sections of thedielectric layer to change a capacitance value of the capacitorstructure between a first end and a second end of the induction coil.20. The vascular stent of claim 19, where a value of the dielectricconstant for the two or more sections increases between the first endand the second end of the induction coil to change the capacitance valueof the capacitor structure between the first end and the second end ofthe induction coil.